After completing a stocktake the inventory update can fail due to network issues or server problems at Shopify.
A full copy of your stocktake is first emailed to your store administrator before attempting the update, so you have a backup of all your scanned data.
Check your email and save the attached CSV file to the device/computer you are using to do the inventory update.
Cancel any ongoing stocktake, and restart it again. Next, import the saved CSV file to the Stock Take app and do another Inventory update.